Apparatus for pipeline isolation

ABSTRACT

An apparatus for pipeline isolation comprising a pipeline isolation tool ( 1 ) having a cylindrical vessel with locking grips ( 21 ) and sealing member ( 19 ) encircling the cylindrical vessel. The locking grips ( 21 ) and sealing members ( 19 ) are operable by a hydraulic piston ( 10 ) contained within a core of the cylindrical vessel and a hydraulic pump for operating the piston ( 10 ). The piston ( 10 ) is a double rodded acting piston ( 10 ) comprising an elongated shaft and a head centrally located on the shaft so that the volume swept by the piston ( 10 ) is equal in both directions. A control module ( 32 ) is connected to the isolation tool ( 1 ) at one end and a gauging tool ( 33 ) is connected to the other end of the isolation tool ( 1 ).

The present invention relates to an apparatus for pipeline isolation andin particular to an apparatus for plugging high interior pressurepipelines.

Oil and gas are useful and expensive commodities that are transportedfrom source to secondary locations using long lengths of pipe known aspipelines. Generally throughout the lifetime of the pipeline, repairs orreplacement of sections must occur. However some if not all of thepipelines are situated entirely or in part in a difficult workingenvironment, for example on the seabed. This fact encompassed with highpressured pipeline interiors meant that pipeline isolation was adifficult and arduous task, as traditionally pipelines requiringisolation had to be depressurised prior to any work commencing.

U.S. Pat. No. 4,332,277 discloses the Wittman tool which enablesisolation of a high pressure pipeline. It is therefore unnecessary todepressurise an entire pipeline resulting in significant cost savings bythe pipeline owners.

However, there is a significant disadvantage to the Wittman tool. Thetool “control function” is conducted using a hydraulic tether. Thehydraulic tether only functions effectively using a short rangehydraulic control umbilical. This prevents the Wittman tool fromventuring great distances into the pipeline. Thus the tool is operatedclose to the beginning or end of the pipeline.

Recent developments in magnetics technology enabled “through thepipeline wall” communication using Extremely Low Frequency (ELF). ELF isbased on excitation and detection of low frequency magnetic fields.Magnetic waves or fields are found at the lower end of the frequencyspectrum between O Hz and 300 Hz.

Extremely Low Frequency (ELF) magnetic waves are found at the lower endof the magnetic frequency spectrum and can be used to penetrate throughCarbon Steel, concrete earth, water etc. independently of most physicalmediums between transmitter and receiver. ELF has not been usedextensively by the military for signal traffic because its datatransmission rate is too slow. Some ELF technology remained classifiedby the military until the mid 90's.

Very Low Frequency communications (VLF) using magnetic waves or fieldshave been used for over forty years as a method for transmittingmessages to and from submarines. For example, shoreside VLF transmittersbased in the United Kingdom can broadcast signal traffic to submarinesbased in Singapore provided the submarine is fitted with a VLF aerialand is trailing at a shallower depth than 25 feet or is manoeuvring atperiscope depth.

Ultra Low Frequency (ULF) enabled the US to adopt a more sophisticatedbroadcast network as part of the US Sanguine operation, where twotransmitters with enormous aerial systems were maintained. The twotransmitters could broadcast ULF signals to US fleet submarines atdeeper depths worldwide.

ELF communication techniques enabled the development of autonomouspipeline isolation tools (plugs) that do not require an umbilicaltether, thus allowing remote isolation of a pipeline at any chosenlocation along that pipeline, even hundreds of miles away from theisolation tool's initial launch point. The command functions carried outby the isolation tool, such as locking, monitoring and unlocking arecarried out by an ELF communication system operating through thepipeline wall.

Despite this there are problems associated with the autonomous pipelineisolation tool. Initially most tools contain a conventional pistonwithin the isolation tool, whereby the rod side of the piston has alesser volume than the flat side of the piston. This imbalance within aclosed hydraulic system requires installation of an accumulator or othercompensating device to house the additional oil volume presented byhaving a rod on one side of the piston and no rod on the other side ofthe piston.

A further problem occurring is the inability to check that the isolationtool will reach the desired location prior to an isolation operationcommencing without using a separate dedicated gauging tool. It is costlyto employ a separate dedicated gauging tool to determine that theinternal pipeline geometry is sound and free, but it is also costly ifduring an operation it is discovered that the internal pipeline geometryis unsound and is blocked by an obstruction. Secondly, in order toensure that an isolation tool can be recovered from a failure or “deadship” situation, it is necessary to install a master dump valve. Whilstit is essential to incorporate the master dump valve, it is extremelyundesirable as it competes for space within the isolation tool. Thirdly,smaller pipelines prove to be more difficult to build isolationapparatus for, as the electronic and hydraulic controlling componentsmust be enclosed within reduced pressure vessel containers.

It is an object of the present invention to seek to alleviate theaforementioned problems.

Accordingly, the present invention provides an apparatus for pipelineisolation composing a pipeline isolation tool having a cylindricalvessel with locking grips and sealing members encircling the cylindricalvessel and being operable by a hydraulic piston contained within a coreof the cylindrical vessel and a hydraulic pump for operating the pistonwherein the piston is a double rodded acting piston comprising anelongated shaft and a head centrally located on the shaft so the volumeswept by the piston is equal in both directions.

Preferably, a control module is connected to the isolation tool at oneend thereof.

Ideally, a plate member is provided on the control module and a masterdump valve is incorporated into the plate member.

Preferably, a trigger spool valve is incorporated into the plate memberin order to prevent the master dump valve from operating until theisolation tool is at a final destination point within the pipeline.

Ideally, the trigger spool valve is driven from a pilot line on thehydraulic pump which is activated when the isolation tool reaches itsfinal destination point, thereby pressurising the pilot line and drivingthe trigger spool valve away from the master dump valve allowing themaster dump valve to activate in response to a pressure spike.

Preferably, the attached control module has means for communication witha remote unit.

Ideally, the said control module is adaptable for use with a range ofisolation tools having different external diameters.

Preferably, the actions of the double rodded acting piston arecontrollable by signals from the remote unit, the signals beingcommunicatable through the pipeline to the control module usingextremely low frequency magnetic waves.

Ideally, the magnetic waves are detectable and transmittable using anaerial array cluster.

Preferably, movement of the isolation tool during isolation is detectedusing scintillating detectors disposed in the remote unit, thescintillating detectors being tuned for frequency recognition ofspecific radioactive isotopes disposed in the control module.

Ideally, the remote unit is a programmable autonomous underwater vehicle(AUV) having an on-board ELF communications system.

Preferably, one end of the rod of the double-shafted piston is hollow.

Ideally, machined components of the apparatus are manufactured fromtitanium or a titanium alloy.

Preferably, a gauging tool is provided at the end of the isolation tooldistal from the control module.

Ideally, two or more isolation tools are provided between the controlmodule and the gauging tool.

The present invention also provides a control system for controlling theoperation of an apparatus for pipeline isolation as outlined above,comprising a first module disposed in the control module including afirst microcontroller for monitoring output values from pressuresensors, valve controllers, a hydraulic pump motor and power supplies, asecond module disposed in a remote unit comprising a secondmicrocontroller for monitoring output values from scintillatingdetectors, the first and second microcontrollers each having acommunication means for communicating through a pipeline using ELF andthe second module being capable of communicating with a remote commandunit.

The present invention also provides a control program for controllingthe system as outlined above, comprising interrogation means formonitoring output values received from the pressure sensors, the valvecontrollers, the hydraulic pump motor, scintillating detectors and thepower supplies, interpretation means for analysing output valuesreceived from the interrogation means and means for generating andtransmitting signals both in response to output values received from theinterrogation means and in response to pre-programmed operatinginstructions to operate the valve controllers and the hydraulic pumpmotor to set and unset the isolation tool.

Preferably, the interpretation means further includes alarm-generatingmeans operable if output values from the pressure sensors fall outsidepre-programmed allowable bandwidths after the isolation tool is set.

Advantageously, front and rear portions of the isolation tool containball joint housings which enable attachment of further tools.

Advantageously, a gauging tool is attached to the isolation tool wherethe gauging tool contains gauge plates which record the geometry of thepipelines.

It is preferable for the gauging tool to carry gauging plates suitablefor the particular pipeline being isolated and for the gauging plates tohave geometry in excess of the isolation tools external diameter.Ideally, the gauge plates are configured to accommodate 92% of internaldiameter of the targeted pipeline however the gauge plates can be madeto accommodate an individual clients requirements. Ideally, the gaugingtool is detached from the isolation tool prior to the isolationoperation commencing and is deployed down the pipeline to confirm thatthe internal pipeline is sound and free from obstruction.

Preferably, the gauging tool is recoupled with the isolated tool priorto the pipeline isolation operation commencing.

Ideally, the isolation apparatus is conveyed to the isolation point in a“train” by the movement of a fluid within the pipe. Advantageously, the“train” comprises a gauging tool, one or more isolation tools and acontrol module. Ideally, once the isolation tool or tools are at theisolation site, a command system in combination with a communicationsystem external to the pipeline communicates with the control moduleinside the pipeline using ELF techniques.

Ideally, the remote unit activates the double-action or double-shaftpiston and the plugging members are engaged provided conditions withinthe pipeline are appropriate. Advantageously, the double action pistonis readily adaptable to suit a wide range of sizes of isolation tools.Advantageously, the isolation tool is also readily adaptable toaccommodate pipelines with various internal diameter sizes. For example,pipeline internal diameters generally range from 0.30 m to 1.07 m andthe isolation tool can be made to specific requirements. Ideally, thesame control module can be adapted to various sized isolation tools.

The invention will now be described more particularly with reference tothe accompanying drawings, which show by way of example only severalembodiments of an isolation tool of the invention.

In the drawings,

FIG. 1 is a cross-sectional side view of a first embodiment of anapparatus according to the invention;

FIG. 2 is a cross-sectional side view of a first embodiment of anisolation tool;

FIG. 3 is a cross-sectional side view of the first embodiment ofisolation tool in an unset configuration within a pipeline;

FIG. 4 is a cross-sectional side view of the first embodiment ofisolation tool in a partially set configuration within a pipeline;

FIG. 5 is a cross-sectional side view of the first embodiment of theisolation tool in a fully set configuration within a pipeline;

FIG. 6 is a perspective view of a plate member of the control module;

FIG. 6 a is an end view of the plate member of FIG. 6;

FIG. 6 b is a perspective view of a master dump valve within the platemember of FIG. 6;

FIG. 7 is a cross-sectional end view of the master dump valve of FIG. 6in an unset position prior to operation;

FIG. 7 a is a cross-sectional end view of the master dump valve of FIG.6 in a partially set position during operation;

FIG. 7 b is a cross-sectional end view of the master dump valve of FIG.6 in a set position during operation;

FIG. 7 c is a cross-sectional perspective view of the master dump valveof FIG. 6 in a set position during operation;

FIG. 8 is a perspective view of a pressure head support disk;

FIG. 8 a is an end view of the pressure head support disk of FIG. 8;

FIG. 9 is a cross-sectional side view of a second embodiment of anisolation tool;

FIG. 10 is a cross-sectional side view of a double shafted piston;

FIG. 11 is a perspective view of the first embodiment of isolation toolas shown in FIG. 2;

FIG. 12 is a perspective view of a third embodiment of isolation tool;

FIG. 13 is a schematic drawing of a command system, a communicationsystem and a control system of the apparatus; and

FIG. 14 is a schematic diagram of an electronic circuit board for atransceiver.

Referring initially to FIG. 1, there is shown a cross-sectional sideview of a preferred embodiment of the apparatus of the inventioncomprising four modules in a train where the front end first module is agauging tool 33, the second and third modules are isolation tools 37 and38 respectively and the rear end fourth module is a control module 32.The gauging tool 33 is the first module to travel downstream 36 at thebeginning of a pipe isolation project, into a region of high pressure30. The gauging tool 33 houses gauge plates which will confirm if thepipeline geometry is negotiable prior to launching the isolation tools37 and 38 respectively. The gauging tool 33 is uncoupled from the trainand launched down the pipeline on it's own. The gauging tool 33 is thenrecovered further down the line (or recovered to the launcher) and therecovered gauge plates are examined. Once it is decided that the line isclear and the train can reach the isolation location, the gauging tool33 is re-coupled to the train and the train is launched.

There are pressure transmitters located on the train within thepipeline. The pump pressure transmitter is situated on the controlmodule 32. There are pressure transmitters 41-44 on the isolation tools37 and 38 respectively. Essentially these pressure transmitters 41-44record and transmit the pressure of the double-shafted hydraulic pistonin the set and unset positions. Pressure transmitters 41 and 43 recordand transmit the pressure of the double shafted hydraulic piston in theset position and pressure transmitters 42 and 44 record and transmit thepressure of the double shafted hydraulic piston in the unset position onisolation tools 37 and 38 respectively.

There are further pressure transmitters located on the train in thepipeline. When the train is in the pipeline it is possible to measurethe pressure downstream 36, the annulus pressure 35 and upstreampressure 34 from the train. In this particular example, the downstreampressure is recorded and transmitted by pressure transmitter 47, whilstpressure transmitters 46 and 45 record and transmit the annulus andupstream pressures respectively.

The operation of isolation tools 37 and 38, and control module 32 shallbe explained clearly with reference to FIGS. 2-12 and FIGS. 13-14respectively.

FIG. 2 is a cross-sectional side view of a first embodiment of anisolation tool 1. The isolation tool 1 comprises a closed hydraulicsystem, ball joint housings 15 and 24 at the forward and rear endsrespectively, a pressure head 14, a pressure head support disk 17, apacker seal 19, a grip bearing ring 12, a grip segment 21, an actuatorflange 22 and an actuator flange support disk 23. The closed hydraulicsystem comprises a double shafted hydraulic piston 10, return springcentralising pins 11, return spring receptacle 13, a cylinder head 20,piston cylinder 16 and a radioactive isotope (not shown) is located inthe isolation apparatus for detection purposes.

The closed hydraulic system is centrally situated within the isolationtool 1. The front 10 a of the double shafted hydraulic piston 10 isencased by the pressure head 14, which has two protruding members whichextend rearwardly encasing the forward half of the closed hydraulicsystem. The first protruding member 14 a is positioned between thepiston cylinder 16 and the return spring receptacle springs 13, whilstthe second protruding member 14 b is positioned outside the outer returnspring receptacle springs 13 and the forward protruding member 22 a, andis enclosed by both the packer seal 19 and the grip bearing ring 12. Thepressure head 14 has a ball joint housing 15 attached to the forwardside. The pressure head 14 is held securely in position by the pressurehead support disk 17. The rear 10 b of the double shafted hydraulicpiston 10 is encased by both the actuator flange 22 and the rear balljoint housing 24. The actuator flange 22 has a forward protruding member22 a which encases the rearward half of the closed hydraulic system. Theforward protruding member 22 a is positioned such that it is outside thereturn spring receptacle springs 13 and inside the second rearwardlyprotruding member 14 b.

The actuator flange 22 is held securely in position by the actuatorflange support disk 23. Further support is provided to the actuatorflange 22 and the grip bearing ring 12 by the grip segment 21. Theisolation tool 1 is launched down the pipeline and propelled by fluid tothe required location.

The movement of the isolation apparatus is monitored and detected usingELF techniques. A battery powered ELF pinger is placed inside a controlmodule. The position of the isolation apparatus inside the pipeline islocated by searching with an ELF detector on the outside of the pipelinefor the ELF pinger inside the pipeline. The precise location of theisolation apparatus can be detected due to the fact that the ELF signaldecays rapidly with distance. The closer the pinger is situated to theaerial placed outside the pipeline, the stronger the ELF signal receivedby this aerial. This means that the pinger cannot be detected until thedistance between the pinger and receiver is less than around 4-10metres, depending on background noise conditions. Once at the desiredlocation, the isolation tool 1 is remotely operated to plug the pipe,(this requires a far more sophisticated transmitter, receiver which willbe discussed fully later). Remote commands mechanically engage a motordriven pump which pressurizes fluid contained within the closedhydraulic circuit. This fluid is used to move the double shaftedhydraulic piston 10 in one direction to set the isolation tool 1 and tomove the double shafted hydraulic piston 10 in the other direction tounset the isolation tool 1.

FIGS. 3 to 5 provide detailed cross-sectional side views of the firstembodiment of the isolation tool 1 of FIG. 2 in an unset, partially setand fully set configuration within the interior of a pipe. In FIG. 3,the isolation tool 1 is in an unset configuration and sits on the lowersurface of the pipe wall 25. The double shafted hydraulic piston 10engages forcing the return springs held on the return springcentralising pins 11 into a compressed position. FIG. 4, shows the gripsegment 21 which encircles the isolation tool 1 being forced intocontact with interior circumferential surface of the pipe wall 25 as thesprings compress. The grip segment 21 is the only member of theisolation tool 1 in contact with the interior circumferential surface ofthe pipe wall 25 in this partially set configuration. FIG. 5 showsfurther compression of the return spring receptacle springs 13. Thisforces the packer seal 19 into contact with interior circumferentialslice of the pipe wall 25. The piston geometry was redesigned such thatthe double shafted hydraulic piston 10 had a rod on both sides of thepiston face, thus bringing the piston into fluid balance. The rodhollowed out of the forward end 10 a (see FIG. 2) of the double shaftedhydraulic piston 10 enables the trapped gas to be compressed into acavity of much greater volume than in the prior art.

FIGS. 6 and 6 a are perspective and end views respectively of the platemember 4, where the plate member 4 has a built in master dump valve 401.FIG. 6 b is a perspective view of the master dump valve 401 within theplate member 4. All of the hydraulic and annulus fluid pipework mustpenetrate the plate member 4, thus considerable space is saved withinthe isolation tool 1. The master dump valve 401 operates on the‘pressure spike’ principle. Once the pressure increases to a level thatis equal to or greater than a preset value in excess of the pipelinesoperating pressure, the master dump valve pressure relief valve sensesit and activates the master dump valve 401.

It is possible for the remotely operated isolation apparatus to getcaught on a weld head or some other obstruction projecting from insidethe pipeline. Such a stoppage could cause a pressure spike in thepropelling fluid behind the isolation apparatus which in turn wouldcause the activation of the master dump valve 401. In order to preventthe master dump valve 401 from operating inadvertently an additionaltrigger spool valve 400 blocking the sensor is provided. FIGS. 7 to 7 care cross-sectional end views of the master dump valve 401 and triggerspool valve 400 positioned within the plate member 4, where the masterdump valve 401 and trigger spool valve 400 are in pre activation,partial activation and post activation settings. FIG. 7 shows thetrigger spool valve 400 built into the sliding spool 404 of the masterdump valve 401. The trigger spool valve 400 prevents the sliding spool404 of the master dump valve 401 from moving until the isolation tool 1is at the final destination point within the pipeline.

The trigger spool valve 400 is driven from a pilot line on the hydraulicpump. FIG. 7 a shows the movement of the trigger spool valve 400 onactivation of the hydraulic pump. Once the hydraulic pump is activated,it pressurises a pilot circuit which drives the trigger spool valve 400away from the sliding spool 404 of the master dump valve 401. Thetrigger spool valve 400 is then itself locked by a spring loadedlatching detent 402. Once the trigger spool valve 400 is latched, thesliding spool 404 of the master dump valve 401 is free to operate,should it see a pre-determined pressure spike increase above pipelineoperating pressure. FIGS. 7 b and 7 c show the position of the slidingspool 404 of the master dump valve 401 once it is operational. Theoperational position of both the sliding spool 404 of the master dumpvalve 401 and the trigger spool valve 400 cause end pieces to projectbeyond the circumferential rim of the plate member 4. The end pieces areprotected by other members of the isolation tool 1 that have a diameterthat is greater than the diameter of the combined plate member 4 and endpieces of the sliding spool 404 of the master dump valve 401 and thetrigger spool valve 400.

FIGS. 8 and 8 a are perspective and end views respectively of thepressure head support disk 17 which is positioned on the isolation tool1 remote from the plate member 4.

FIG. 9 is a cross-sectional side view of a second embodiment ofisolation tool 2 showing the shape of the double shafted hydraulicpiston 101. FIG. 10 is a magnified cross-sectional side view of thedouble shafted hydraulic piston 101, which operates as previouslydescribed.

FIGS. 11 and 12 are perspective views of the isolation tool. FIG. 11shows the preferred embodiment of the isolation tool 1, where thepressure head support disk 17 and the actuator flange support disk 23extend beyond the width of the main body of the isolation tool 1providing a measure of protection for the isolation tool 1 as ittraverses through the pipeline.

FIG. 12 is a perspective view of the third embodiment of isolation tool3. The support disks do not extend beyond the width of the main body ofthe isolation tool 3. Instead protection for the sides of the isolationtool 3 is provided by a circular ring of sprung wheels, at the front andrear of the isolation tool 3.

FIG. 13 is a schematic drawing of the command system 4, communicationsystem 5 and control system 6 of the apparatus. A remotely operatedisolation tool 1, (see FIG. 2) is transportable down a sub-sea pipelinefor distances up to and greater than 100 km. It is then autonomouslyoperated to safely seal the product inside the downstream side of thepipeline, prior to intervention works taking place on the upstream sideof the pipeline isolation. The System is structured as follows:

-   -   Command System 4—positioned on a vessel above the sea or        remotely located on the shore    -   Command System 5—positioned on top of the pipeline in use    -   Control System 6—positioned in control module 32, inside the        pipeline in use

All operations of the isolation tool (1) are controlled by a computer206 running software that sends commands and receives readings via thecommunication system 5 comprising first electronics module 301 a andfirst aerial 302 a disposed in a remote unit outside the pipeline andsecond electronics module 301 b and second aerial 302 b disposed in thecontrol module (32) of the isolation apparatus train inside thepipeline. The computer 206 is located on a surface vessel and isconnected to the first electronics module 301 a through an RS485 adaptor205 and a sub-sea umbilical cable 203. Alternatively, the computer 206is located on land and signals are transmitted to the first electronicsmodule 301 a of the communication system 5 via acoustic signaltransmission technology.

The command system computer 206 is mains powered 200 and 201. Thecommand system 4 also sends 24v DC 202 down the sub sea cable 203 to thefirst electronics module 301 a of the communication system 5. The firstelectronics module 301 a and first aerial 302 a of the communicationssystem 5 is placed outside the pipeline and is precisely positionedusing scintillating detectors to enable the matched aerial 302 a tocommunicate optimally with the matched aerial 302 b inside the pipeline.The aerial 302 a comprises a cluster of coils, which form an array as agreater collective transmission source is easier to receive (in magneticterms) by the matched aerial 302 b inside the pipeline and also agreater collective receiver system is beneficial to the single aerial302 b transmitter.

Scintillating detectors determine exact positioning of the isolationapparatus inside the pipeline. These are configured for the isotopes (anexample of isotopes used are Tantalum 182, Iridium 192 or Cesium 137)normally used in isolation apparatus. The scintillating detectors areincorporated inside the aerial array 302 a in pre-defined “optimum”geometry, which facilitates “best transmission and reception” for thecommunication system 5 and control system 6. The scintillating detectorsystem is configured with a twin scintillating detection system so thatany movement of the radioactive isotope in the isolation apparatus isdetected. One detector is always looking at a shining source, and thesecond detector is one metre away looking at a “non shining” source.Should the apparatus move, then the first detector loses its signal andthe second detector gains a signal. This method gives positiveindication that the isolation apparatus has moved.

Alternatively, detectors are hired from third party companies. Theseunits comprise specialist equipment, which are lowered to the seabedonto the pipeline and are moved around by divers or alternative methodsto positions which are beneficial to the external aerial 302 a array.

Optimum positioning is achieved by the aerial system's “in built”scintillating detectors locating on the radiating isotope located in thecontrol module (32). The communications system 5 contains an ELFtransceiver comprising first electronics module 301 a and first aerial302 a for communication with the transceiver of the control system 6comprising second electronics module 301 b and second aerial 302 b.Control system 6 for the isolation apparatus is located inside aone-atmosphere pressure vessel 17, (see FIG. 8) which is located in thecontrol module (32). Through ELF communications, instructions aretransmitted and received to operate the hydraulic pump system 307 to SETor UNSET each of the isolation tools. The control system 6 also sendsinformation on the communication system 5 regarding valve positions308-310, pressure sensor readings 40-47 as well as any alarm status. Thecontrol system 6 enables bandwidths to be set to initiate an alarm,should pressures move outside defined limits, after the isolation tool(1) is SET.

FIG. 14 is a schematic diagram of an electronic circuit board 301 b fortransmitting and receiving ELF signals. Central to the electroniccircuit board 301 b is a PIC18C452 micro-controller 3013. This devicehas built in RAM, ROM and IO. It also has several built in peripheralsincluding a 12C master module, a USART and analogue to digitalconverter. The 12C protocol is used for communications with localdevices on the Printed Circuit Board (PCB) 301 b. The 12C devices on thePCB 301 b include an 8-channel 12-bit A/D converter 3011, a real timeclock, a non-volatile EEPROM, a 4-channel digital potentiometer and an8-bit 4-channel D/A converter 3012.

The micro-controller 3013 uses its USART to communicate with the valvecontrollers through an RS232 interface device and communicates withexternal devices through an RS485 interface device. The pressuretransmitters have a 4 to 20 mA interface and are read using the 12C8-channel 12-bit A/D converter 3011. The ELF transceiver circuitconsists of a push-pull transmitter 3021 and a high gain receiver 3019.The ELF transmitter 3021 is a FET transistor driven digital bridgecircuit, which drives current through the transmitter coil in thedirection and speed determined by the micro-controller 3013 using twoI/O lines. A range of frequencies or phase modulation can be achieved bythe micro-controller by changing the delay between each toggle of theI/O lines.

The ELF receiver circuit takes the signal picked up by the aerial 302 b,amplifies it using amplifier 3018 and uses various band pass filters3017 to remove un-wanted signals. To adapt to different environments andsignal strengths, the micro-controller 3013 can adjust the amplifiergain 3016 from 0 to −80 dB using the 12C 4-channel digitalpotentiometer. The resulting signal is fed into an A/D channel in themicro-controller 3013, which is used to monitor signal levels. Thesignal is also fed into a comparator 3015 set for zero cross overdetection. The resulting signal is a digital representation of the ELFsignals received, and the output is fed into one of themicro-controller's I/O ports for interpretation by software.

Ideally the command system software runs on an IBM compatible PC withthe Microsoft Windows XP operating system. The software is written inVisual C++ and uses standard Microsoft objects and foundation classes.The software has a visual front with mouse and keyboard feedback.Microsoft windows and Visual C++ are event driven and react to keyboard,mouse and communications port events. The Command System software isembedded in the micro-controller. All functions are written in ANSIcompliant C and compiled using the Microchip MCC18 compiler. Forflexibility and ease of maintenance, the Control System PCB and softwareare identical. Changing the digital state of the mode pin on the PCB isall that is required to change the mode of operation. A very simpleFrequency Shift Keying (FSK) method has been implemented, in that “1” istransmitted as one cycle of a 12 Hz wave, and a “0” is transmitted asone cycle of a 6 Hz wave. This coding method works well and is extremelysimple to decode accurately.

If the ELF receiver, the incoming signal must be decoded to determinethe message content in terms of “0”s and “1”s. This is done as follows:

-   a. The incoming ELF signal is hard limited by using maximum    amplifier gain.-   b. The time between each zero crossing of the signal is measured.-   c. The bit type is determined by timing the period between each zero    crossing.

This very simple method implies that the transmitter and receiverantennas 302 a, 302 b should be oriented and aligned in phase. This doesnot present any problem in practical application, as the direction ofthe isolation tool in the pipeline is known, as is the polarity of theexternal antenna.

Each ELF message is made up of only 3 bytes, but in order to preventerroneous communication, extra bit packing is added at transmission. Thereceiver micro-controller checks for a valid packet each time a bit isreceived. In order for the message to be processed, the packet muststart with 7 1-bits and end with 7 0-bits. The data bytes areaccompanied by a Cyclical Redundancy Check (CRC) that must match the CRCcalculated by the receiver. In order to prevent random data generating astart and stop sequence, the data bytes and CRC are split up intonibbles and separated by a O-bit, 1-bit sequence. Steps are taken toensure data integrity. The message format for the ELF communication linkconsists of a total of 64 bits organised as follows:

-   a. 7 consecutive 1-bits start pattern-   b. A 0-bit, 1-bit nibble separator-   c. Data byte 0 most significant nibble-   d. A 0-bit, 1-bit nibble separator-   e. Data byte 0 least significant nibble-   f. A 0-bit, 1-bit nibble separator-   g. Data byte 1 most significant nibble-   h. A 0-bit, 1-bit nibble separator-   i. Data byte 1 least significant nibble-   j. A 0-bit, 1 bit nibble separator-   k. Data byte 2 most significant nibble-   l. A 0-bit, 1-bit nibble separator-   m. Data byte 2 least significant nibble-   n. A 0-bit, 1-bit nibble separator-   o. CRC byte most significant nibble-   p. A 0-bit, 1-bit nibble separator-   q. CRC byte least significant nibble-   r. A 0-bit, 1-bit nibble separator-   s. 7 consecutive 0-bits stop pattern

The micro-controller has an interrupt service routine that processes allhardware interrupts. The ELF zero cross signal causes one of theseinterrupts and when it does, the time between this interrupt and theprevious signal is calculated. Based on two time envelopes, a 0 or 1 bitis clocked into a 64 bit (8 byte) buffer organised as a shift register.The micro-controller does not count the bits received but just checksthe buffer for a valid start, stop and nibble separators. After a validpacket has been received, a function extracts the data and CRC and goeson to process the message.

If a packet is received that is not valid or has some errors, thesoftware will ignore it and will not transmit a response. A lack ofresponse within a preset time is interpreted by the sender as NonAcknowledgment (NACK) and a re-transmission is attempted. When a validpacket is received a flag is set to inform a function running in theforeground that there is a command to execute. Once the command has beenprocessed, an acknowledge message is transmitted back to the sender. TheAcknowledgment (ACK) messages are in the same format as the commandmessages with three bytes and a CRC.

Due to the very low frequency used for ELF communication, the time toprocess messages and execute commands is negligible compared to the timerequired to transmit and receive each message. The messages/commands aresent from the command system 4, (FIG. 13) to the communication system 5,(FIG. 13) to the control system 6, (FIG. 13). The communication system 5acts like an ELF modem. When it receives messages/commands intended forthe control system 6, it will re-package these and transmit them overthe ELF. The responses received from the control system 6 over the ELFor notification of lack of response are also passed back to the commandsystem 4 via the communication system 5. The responsibility forre-transmission and ACK/NACK processing is the responsibility of thecommand system 4. The communication system 5 has two built-inscintillation detection devices. Special operator commands on the PC ofthe command system 4 are used to control and monitor these devices. Thecommands are processed internally and are not transmitted beyond thecommunication system 5 to the control system 6.

It will of course be understood that the invention is not limited to thespecific details as herein described which are given by way of exampleonly and that various alterations and modifications may be made withoutdeparting from the scope of appended claims.

1. An apparatus for pipeline isolation comprising a pipeline isolationtool (1) having a cylindrical vessel with locking grips (21) and sealingmembers (19) encircling the cylindrical vessel and being operable by ahydraulic piston (10) contained within a core of the cylindrical vesseland a hydraulic pump for operating the piston (10) wherein the piston(10) is a double rodded acting piston (10) comprising an elongated shaftand a head centrally located on the shaft so that the volume swept bythe piston (10) is equal in both directions.
 2. An apparatus as claimedin claim 1, wherein a control module (32) is connected to the isolationtool (1) at one end thereof.
 3. An apparatus as claimed in claim 2,wherein a plate member (4) is provided on the control module (32) and amaster dump valve (401) is incorporated into the plate member (4).
 4. Anapparatus as claimed in claim 3, wherein a trigger spool valve (400) isincorporated into the plate member (4) in order to prevent the masterdump valve (401) from operating until the isolation tool (1) is at afinal destination point within the pipeline.
 5. An apparatus as claimedin claim 4, wherein the trigger spool valve (400) is driven from a pilotline on the hydraulic pump which is activated when the isolation tool(1) reaches its final destination point, thereby pressuring the pilotline and driving the trigger spool valve (400) away from the master dumpvalve (401) allowing the master dump valve (401) to activate in responseto a pressure spike.
 6. An apparatus as claimed in claim 2, wherein theattached control module (32) has means for communication with a remoteunit (4).
 7. An apparatus as claimed in claim 2, wherein the saidcontrol module (32) is adaptable for use with a range of isolation tools(1) having different external diameters.
 8. An apparatus as claimed inclaim 6, wherein the actions of the double rodded acting piston (10) arecontrollable by signals from the remote unit (4), the signals beingcommunicatable through the pipeline to the control module (32) usingextremely low frequency magnetic waves.
 9. An apparatus as claimed inclaim 8, wherein the magnetic waves are detectable and transmittableusing an aerial array cluster (302 a, 302 b).
 10. An apparatus a claimedin claim 6, wherein movement of the isolation tool (1) during isolationis detected using scintillating detectors disposed in the remote unit(4), the scintillating detectors being tuned for frequency recognitionof the specific radioactive isotopes disposed in the control module(32).
 11. An apparatus as claimed in claim 6, wherein the remote unit(4) is a programmable autonomous underwater vehicle (AUV) having anon-board ELF communication system (5).
 12. An apparatus as claimed inclaim 1, wherein one end of the rod of the double-shafted piston (10) ishollow.
 13. An apparatus as claimed in claim 1, wherein machinedcomponents of the apparatus are manufactured from titanium or a titaniumalloy.
 14. An apparatus as claimed in claim 2, wherein a gauging tool(33) is provided at the end of the isolation tool (1) distal from thecontrol module (32).
 15. An apparatus as claimed in claim 14, whereintwo or more isolation tools (1) are provided between the control module(32) and the gauging tool (33).
 16. A control system (4, 5, 6) forcontrolling the operation of an apparatus for pipeline isolation asclaimed in claim 1, comprising a first module disposed in the controlmodule (32) including a first microcontroller for monitoring outputvalues from pressure sensors (40 to 47), valve controllers (308, 309,310), a hydraulic pump motor (307) and power supplies (303, 305), asecond module disposed in a remote unit (4) comprising a secondmicrocontroller for monitoring output values from scintillatingdetectors, the first and second microcontrollers each having acommunication means for communicating through a pipeline using ELF andthe second module being capable of communicating with a remote commandunit.
 17. A control program for controlling the system (4, 5, 6) asclaimed in claim 16, comprising interrogation means for monitoringoutput values received from the pressure sensors (40 to 47), the valvecontrollers (308, 309, 310), the hydraulic pump motor (307),scintillating detectors and the power supplies (303, 305),interpretation means for analyzing output values received from theinterrogation means and means for generating and transmitting signalsboth in response to output values received from the interrogation meansand in response to pre-programmed operating instructions to operate thevalve controllers (308, 309, 310) and the hydraulic pump motor (307) toact and unset the isolation tool (1).
 18. A control program as claimedin claim 17, wherein the interpretation means further includes alarmgenerating means operable if output values from the pressure sensors (40to 47) fall outside pre-programmed allowable bandwidths after theisolation tool (1) is set.